1. Field of the Invention
The present invention relates to ultrasonic motors used in a timepiece, a camera, a printer, a storage apparatus and so on, and more particularly to an ultrasonic motor with a magnified drive force.
2. Description of the Related Art
In recent times, in the field of micromechanics attention is attracted to a ultrasonic motor utilizing as power, an elliptical motion as synthesized vibration of elongation and contraction vibration and bending vibration produced in a piezoelectric element applied with a drive signal of alternating current voltage or the like.
Here, an explanation will be given of an ultrasonic motor 4 and an ultrasonic motor 5 as conventional ultrasonic motors in reference to FIGS. 13a and 13b.
As shown by FIG. 13a, the ultrasonic motor 4 is provided with the structure installed with a projection 41 for taking out an output for moving a moving body (illustration is omitted) by being brought into press contact with the moving body at one end face of a piezoelectric element 40 in a shape of a rectangular parallelepiped.
In this case, the piezoelectric element 40 is provided with four of a polarized region 40a, a polarized region 40b, a polarized region 40c and a polarized region 40d which are polarized in the same polarities in the thickness direction and arranged in two rows each comprising two pieces thereof. Further, the polarized regions 40a, 40b, 40c and 40d are respectively provided with electrodes. Further, the electrode on the polarized region 40a and the electrode on the polarized region 40d which are diagonally opposedly positioned, are shortcircuited by using a lead wire. Similarly, the electrode on the polarized region 40b and the electrode on the polarized region 40c are shortcircuited by using a lead wire.
The ultrasonic motor 4 moves the moving body in a positive direction by inputting drive signals to the polarized regions 40a and 40d and moves the moving body in a reverse direction by inputting drive signals to the polarized regions 40b and 40c.
The ultrasonic motor 5 is provided with a piezoelectric element 50 shown by FIG. 13b as a power source. The piezoelectric element 50 is provided with four of a polarized region 50a, a polarized region 50b, a polarized region 50c and a polarized region 50d which are polarized in the same polarities in the thickness direction and arranged in two rows each constituting two pieces thereof similar to the piezoelectric element 40. The polarized regions 50a, 50b, 50c and 50d are respectively provided with electrodes insulated from each other.
The ultrasonic motor 5 moves a moving body, not illustrated, in the positive direction by inputting drive signals X having the same phase to the polarized regions 50a and 50d and inputting drive signals having a phase advanced from that of the drive signal X by 90 degree to the polarized regions 50b and 50c. Further, the ultrasonic motor 5 moves the moving body, not illustrated, in the reverse direction by inputting drive signals having a phase retarded from that of the drive signal X by 90 degree to the polarized regions 50b and 50c.
However, the ultrasonic motor 4 utilizes only a half of the polarized regions of the piezoelectric element 40 as the power source and therefore, large output is not provided.
Further, although the ultrasonic motor 5 utilizes all of the polarized regions of the piezoelectric element 50 as a power source, there is needed a circuit for shifting the phase of the input signal by 90 degree. Particularly, when there is carried out self-excited oscillation for driving the ultrasonic motor by utilizing the self-excited oscillation, two input signals having different phases are used and therefore, the constitution of a self-excited oscillation drive circuit becomes complicated and is difficult to realize.
Further, the ultrasonic motor 4 utilizes the piezoelectric element 40 and the ultrasonic motor 5 utilizes the piezoelectric element 50 as both a source of elongation and contraction vibration and a source of bending vibration and accordingly, large elongation and contraction vibration or bending vibration cannot be provided. That is, sufficient output cannot be provided by the conventional ultrasonic motors 4 and 5. Therefore, in order to provide large output by using the ultrasonic motor 4 or 5, as shown by FIG. 14, for example, a plurality of the ultrasonic motors 4 must be arranged in parallel by using an exclusive jig, which hampers downsizing thereof. Also in this case, vibration escapes from the exclusive jig and, therefore, the output of the ultrasonic motor is reduced.
Further, the elongation and contraction vibration and the bending vibration cannot be controlled independently from each other and accordingly, a moving speed and a drive force of the moving body cannot be controlled widely.